Melanin is a natural pigment found in hair. Melanin and hair-forming cells are naturally produced in the hair bulb at the root of the hair. As new cells are produced, the older ones are pushed upwards out of the skin to form the hair shaft, which is the part of the hair that can be seen above the scalp. Hair can be schematically described as being made of a center part called the cortex, which contains the melanin, and an outer layer called the cuticle. It is the cortex that gives hair its special qualities such as elasticity and curl.
The hair shaft is made of dead cells that have turned into a mixture of different forms of the special hair protein, keratin. Keratin contains high concentrations of a particular amino acid called cystine. Every cystine unit contains two cysteine amino acids in different chains, which have come to lie near each other and are linked together by two sulphur atoms, forming a very strong chemical bond known as a disulphide linkage. This cross-linking by disulphide linkages between the keratin chains accounts for much of the strength of the hair.
Bleaching and dyeing (or coloring) of hair has become increasingly popular over the past years. Younger people may want to change the natural color of their hair to a more fashionable one, while older people may also use dyeing compositions to conceal gray hair. As people grow older, the production of melanin slows, giving more and more gray hair over time. Melanin can be purposely altered by chemical treatments to give lighter shades. The lightening is achieved by oxidizing the melanin pigments, usually with an oxidizing agent in alkaline solution, also called bleaches. Examples of oxidizing agents that can be used are hydrogen peroxide, potassium, sodium or ammonium salts of perborate or percarbonate, persulfate and percarbamide.
Bleaches are also used during oxidative dyeing treatments. Oxidative (or “permanent”) dye compositions comprise “precursor dyes” which are small molecules capable of diffusing into the hair. These molecules mainly belong to three classes of aromatic compounds: diamines, aminophenols and phenols. They are sufficiently small to diffuse in the hair shaft where, once activated by an oxidizing agent such as hydrogen peroxide, they further react with other precursors to form larger colored complexes. Oxidative hair dye compositions commonly contain, in addition to the dye precursors and a source of peroxide, a variety of additional cosmetic and peroxide stabilizing agents.
Oxidizing agents can activate oxidative dye precursors across a range of pH. However, it is known that enhanced dye oxidation can be achieved via the use of a hair-swelling agent (HSA) that can adjust the pH of the oxidizing solution. Such HSA's further enhance the oxidizing and dyeing process by swelling the hair fibers to aid both the diffusion of the peroxide and dyeing agents into the hair and enabling faster, more thorough dye oxidization and hair dyeing. Preferred hair-swelling agents for adjusting the pH of peroxide hair oxidizing compositions are aqueous alkaline solutions containing ammonia (ammonium hydroxide) or monoethanolamine(MEA).
Low levels of chelants are routinely used as stabilizers or preservatives in various oxidizing compositions. For example, EDTA (ethylenediaminetetraacetic acid) is commonly used as a stabilizer in hydrogen peroxide solution, which would otherwise decompose too rapidly and could not be stored for a long time. Ethylene diaminedissucinnic acid (EDDS) is also known as a good stabilizing agent component to increase the stability of laundry bleaching products. Amounts as low as 0.1% by weight of the oxidizing composition are usually used to stabilize the oxidizing agent contained in said oxidizing compositions.
Oxidative treatments of hair such as bleaching (decoloration) and oxidative dyeing give good results and are very commonly used. They are however not without drawbacks. The oxidizing agents used for bleaching and oxidative dyeing damage hair to some extent. The mechanism by which damage is caused to the hair fibers is not perfectly understood. However, it is known that some of the disulphide bonds linking the keratin chains break in the presence of oxidizing compositions. Repeated oxidative treatments leave weak, brittle hairs, which have little shine and luster. An enormous effort has been made to address this problem over the past years, and various solutions have been proposed.
Today, most dyeing or bleaching compositions are sold with a conditioner, which is applied on hair after the bleaching or dyeing composition has been rinsed off. Examples of conditioning agents are silicones, cationic surfactants and cationic polymers. However efficient, conditioners cannot prevent successive chemical treatments causing premature hair breakage. In fact, conditioners do not bring the hair back to its initial condition but merely conceal the damage under a protective layer of the conditioning agent, which only results in an improved feel of the hair.
Attempts have been made to protect the hair from damage instead of merely concealing it. U.S. Pat. No. 5,100,436 discloses hair dyeing compositions comprising metal-chelant complexes. The use of catalytic amounts of dipyridyl or o-phenanthroline complexes (0.001 to 0.1% by weight of the solution) allows a reduction in the time of exposure, thus reducing the damage caused by the oxidizing agent.
U.S. Pat. No. 6,013,250 discloses composition for treating hair against chemical and photo damage by the use of hydrolyzed proteins having an abundance of anionic amino acids and in particular, sulphur-containing amino acids. These proteins serve as “decoys”, in order to minimize the damage caused to the natural disulphide bonds.
U.S. Pat. No. 4,138,478 discloses agents for reducing the damage to hair during bleaching and dyeing by the use of a water-soluble 3-amino-1-hydroxypropane-1,1-diphosphonic compound for protecting hair from damage by “nascent oxygen”. According to this patent, “the diphosphonic compound is substantively adsorbed by the hair and acts to hinder degradation of the hair by nascent oxygen which is either present therewith or which is substantially added”. Other protective compounds such as hydroxyethane-1,1 diphosphonic acid (HEDP) and ethylenediaminetetramethylene phosphonic acid (EDTMP) are disclosed at low levels in U.S. Pat. No. 3,202,579 and U.S. Pat. No. 3,542,918.
“Properties of peroxide-bleached hair” (W. Edman & E. Marti, J. Soc. Cosmet. Chem., 1960, p.133), discloses that an aqueous solution of hydrogen peroxide is stabilized by adding 0.1% by weight of the bleaching composition of tetrasodium salt of EDTA (ethylenediamine tetraacetic acid) and that damage to hair can be prevented by adding 0.1% of the tetrasodium salt of EDTA to the aqueous bleaching compositions. However, is has now been surprisingly found that EDTA, although widely used in bleaching and dyeing compositions, displays very little benefits, unless utilized at levels much higher than 0.1%.
Chelants in hair care compositions have been used to remove minerals bound to hair. For example, U.S. Pat. No. 5,635,167 discloses a process for the removal of exogenous metal ions that have become attached to hair. The treatment comprises a step wherein hair is contacted with a blend of chelating agents (selected from the group consisting of amino acid chelating agents, polyphosphate chelating agents and phosphonate chelating agents) at a pH of between 4 and 9 and at a concentration of between 4% to 25% by weight.
WO97/24106, Dias et al. discloses hair coloring compositions comprising a water soluble peroxygen-bleach, a bleaching aid selected from organic peroxyacid bleach precursors and preformed organic peroxyacids and one or more hair coloring agents. Various chelants are disclosed as optional ingredients and exemplified in hair care compositions at 0.1% by weight of the composition. The organic peroxy acid bleach precursors are defined as organic compounds that react with hydrogen peroxide in a perhydrolysis reaction to produce a peroxyacid. These bleaching aids are claimed to provide benefits including reduced hair damage at lower pH. However, the Applicant has found that at a pH higher than 8, these bleaching aids are much more damaging to hair than usual water-soluble oxidizing agents such as hydrogen peroxide. Without being bound by theory, the Applicant believes that the conjugate base of the organic peroxyacid formed at a pH above 8 is more likely to oxidize the disulphur bonds of the keratin than other oxidizing agents such as hydrogen peroxide. Additionally, hair coloration, especially with oxidative dyes is much poorer at pH 8 than pH 10, which is another advantage of this invention over WO9724106. Finally peroxyacid precursors are difficult to solubilize, especially in oil-in-water emulsion.
Despite these developments, damage to hair caused by the strongly aggressive chemicals contained in most bleaching, dyeing or perming compositions particularly with repeated usage is still a problem, particularly at high pH.
It is hence an object of the present invention to provide new compositions capable of improved protection of keratinous fibers such as human hair from oxidative damage, in particular the structurally important keratin bonds such as the disulphide bonds from oxidative breakage.
It is another object of this invention to provide bleaching, dyeing or perming compositions with a better efficiency in terms of light shade, color evenness, color fading and hair feel.
It is another object of this invention to provide a hair-protecting agent that is non-toxic, even when utilized in relatively large proportions and which is biodegradable.
The Applicant has surprisingly found that chelants having specific Conditional Stability Constants for Copper and Calcium at pH 10 have damage inhibiting properties. The Applicant has also found that diamine-N,N′-dipolyacid or monoamine monoamide-N,N′-dipolyacid chelants were particularly useful at reducing hair damage. None of the above-mentioned references disclose the compositions of the present invention.